Spray material on an iron base and method of manufacturing a spray material as well as thermal spray layer and spraying method

ABSTRACT

The invention relates to a spray material on an iron base for the thermal coating of a substrate, in particular for the thermal coating of a running surface of a cylinder of a reciprocating combustion engine, wherein the spray material includes FeTiO 3  as a base material. In accordance with the invention, the spray material includes at least one first solid lubricant composed of a sulfide and one second solid lubricant composed of a fluoride. The invention further relates to a method for manufacturing a spray material, to a spray wire, in particular a spray filler wire for use in a thermal wire spraying method, to a thermal spray layer on an iron base, in particular for a running surface of a cylinder of a reciprocating combustion engine, to a spraying method for manufacturing a thermal spray layer, as well as to the use of a powder material and of a spray wire for manufacturing a thermal spray layer.

The invention relates to a spray material on an iron base for the thermal coating of a substrate, in particular for the thermal coating of a running surface of a cylinder of a reciprocating combustion engine, to a method of manufacturing a spray material, to a spray wire, in particular a spray filler wire for use in a thermal wire spraying method including a spray material on an iron base, to a thermal spray layer on an iron base for a substrate, in particular for a running surface of a cylinder of a reciprocating combustion engine, to a spraying method of manufacturing a thermal spray layer and to the use of a powder material and of a spray wire for manufacturing a thermal spray layer in accordance with the preamble of the independent claim of the respective category.

Coatings applied by thermal spraying have long been known for a plurality of applications. Surfaces of oil lubricated cylinder running surfaces in vehicle engines have thus already been coated inter alia by plasma spraying for some time, for example, with the layer above all considerably reducing the coefficient of friction which is operative between the piston rings and the cylinder wall, whereby the wear of piston rings and of the cylinder is considerably reduced, which results in an increase in the service life of the engine, in an extension of the service intervals, for example on an oil change, and not least in a noticeable increase in engine performance. This is achieved by different measures. For example, such layers for oil lubricated internal combustion engines can contain deposits of dry-film lubricants in a base matrix, with pores of predefinable size additionally being able to be provided in the base matrix which act as oil pockets and thus, together with the relatively soft deposited dry film lubricants, considerably reduce the friction between the piston rings and the cylinder wall. The base matrix itself which in particular contains the dry film lubricants and the pores among further components is in this respect made up of a hard matrix material which guarantees a high service life of the cylinder running surfaces and of the piston rings. Such a modern high-performance cylinder running surface is described in detail, for example, in EP 1 340 834.

Further typical applications for surfaces applied by thermal spraying are the coating of turbine parts with a wear protection and thermal barrier coatings and the coating of components of oil lubricated bearings such as the coating of crank bearings other workpieces which are subject to particular physical, chemical or thermal loads. Depending on the purpose the layer has to satisfy, very specific materials can be used, as a rule in the form of spray powders or spray wires which have the required specific properties and composition to generate the required properties of the surface layer to be sprayed.

With larger production volumes, the powder material price plays a decisive role with respect to the cost-effectiveness of the coating, in particular in the coming of cylinder running surfaces by means of the plasma spraying process APS, above all in the case of the coating of larger engines (e.g. truck diesel engines).

The production costs of the powder are, on the one hand, dependent on the prices for raw materials and, on the other hand, on the processing effort which is required to process the raw materials to a usable material which is suitable for carrying out the selected process.

In the known atomization of metallic materials (by means of gas or water), the energy costs can practically only be downwardly influenced by a better powder yield. In this respect, the specification of the distribution of the particle size plays a decisive role. Under best conditions, the manufacturing costs of metallic powders in a quality, such as is required for internal coatings of cylinders for internal combustion engines, for atomization can today hardly be reduced below US $10 per kg. It must therefore rather be expected that specific limits apply to a further cost reduction.

On the other hand, the demands on the performance capability of the spray materials are becoming greater as time passes. The tribological properties of the coatings at elevated temperatures are in particular becoming more and more important since the effect of the lubricants considerably reduces as the wall temperature rises. Tribological solutions which can be used up to a wall temperature of 330° C. are generally possible. In this respect, the anti-scuffing properties of the layer materials play a decisive role.

Grinding and screening is generally considered a favorable manufacturing process of powders for thermal spraying, also in the case of larger quantities of ceramic spray materials of metallic oxides. In the case of certain materials, minerals in the powder can be processed without additional melting.

Iron titanate FeTiO₃, which is also known as ilmenite, has previously already been considered as a potential material for cylinder running surfaces. Ilmenite is formed from approximately 53% TiO₂ and 47% FeO, and crystallizes in a hexagonal crystal system. The hardness of ilmenite crystals amounts to approximately 650 HV, that is values of 400 to 500 HV are possible in the layers with optimized parameters.

An ilmenite spray material was therefore already proposed in UA 74 987 for forming corrosion-resistant coatings by mean of thermal spraying processes. In WO 2004/106711, the applicants propose ilmenite, partly in combination with other metal-ceramic materials and/or oxides, as a spray material for coating cylinder running surfaces of turbocharged engines However, these coatings are not designed for the increasing tribological demands at high or highly fluctuating temperature loads, but mainly improve the hardness or the corrosion resistance of the coated surfaces.

It is therefore the object of the invention to provide a new spray material in the form of a powder material or in the form of a spray wire, in particular a spray filler wire, for the thermal coating of a substrate which can, on the one hand, be manufactured substantially less expensively than the known spray materials and wherein layers sprayed therewith above all have excellent tribological properties, simultaneously in different temperature ranges, so that the powder material is above all suitable for forming friction-optimized running surfaces on cylinders of reciprocating combustion engines which are also operated under changing load conditions. In this respect, the surface layers formed using the spray material should in addition be sufficiently corrosion resistant and have an excellent hardness.

It is furthermore an object of the invention to provide a method of manufacturing a corresponding spray material as well as a thermal spray layer, a spraying method for manufacturing a thermal spray layer as well as the use of a powder material or of a spray wire for manufacturing a thermal spray layer.

The subjects of the invention satisfying these objects are characterized by the features of the independent claim of the respective category.

The respective dependent claims relate to particularly advantageous embodiments of the invention.

The invention thus relates to a spray material on an iron base for the thermal coating of a substrate, in particular for the thermal coating of a running surface of a cylinder of a reciprocating combustion engine, wherein the spray material includes FeTiO₃ as a base material. In accordance with the invention, the spray material includes at least one first solid lubricant composed of a sulfide and one second solid lubricant composed of a fluoride.

It can thus be demonstrated for the first time by the present invention that spray materials on an iron titanate base, that is on a base of so-called ilmenite having the chemical formula FeTiO₃, are especially suitable in particular for the thermal coating of components of internal combustion engines when at least one sulfide and one fluoride are added to the ilmenite as solid lubricants. The layers thus manufactured are in this respect characterized by an excellent resistance with respect to adhesion wear. The addition of solid lubricants including at least one sulfide and one fluoride, but also especially additionally one nitride, in this respect allows a considerable increase in the wall temperature of cylinder running surfaces in the operating state so that the layers manufactured from a layer material in accordance with the invention are also particularly well suited for use in adiabatic engines.

It is namely ensured by the simultaneous use of at least one sulfide and one fluoride in the spray material in accordance with the invention that the thus thermally sprayed layers have respectively comparably good tribological properties in different temperature ranges.

The tribological performance capability of the iron titanate FeTiO₃ layers (ilmenite) is in this respect substantially improved in accordance with the invention by the direct addition of solid lubricants. The properties of these lubricants are inter alia based on the special crystal structure and on the low tendency to chemical bonds or reactions with metallic and ceramic materials. The specific class of solid lubricants is selected in accordance with the invention in accordance with the temperature loads to be expected. In the case of internal cylinder coatings in internal combustion engines, the highest wall temperature, for example in the contact zone cylinder running surface/piston ring, is advantageously considered for this purpose.

The solid lubricants on a sulfide base, for example MoS₂ and/or WS₂ can be used without problem up to a temperature of 350° C. in an oxidizing atmosphere. In the case of shock loads in internal combustion engines, however, hot contact points can form, e.g. between the cylinder running surface and the piston rings, with the local temperature being able to be considerably higher than 350° C. In accordance with the present invention, at least one further type of solid lubricant is therefore additionally used which has an elevated temperature resistance and is simultaneously chemically resistant under the aggressive chemical conditions in the combustion space and additionally positively influences the adhesion capability and hardness of the coating.

In addition to the fluorides, solid lubricants on a nitrogen base can also particularly advantageously be considered, for example hexagonal BN or CrN, since they also satisfy their functions as solid lubricants up to maximum temperatures of 950° C., also under oxidizing conditions, with such high temperatures frequently also only occurring locally in cylinders of internal combustion engines, for example.

In the specific application case of adiabatic diesel engines, even higher local contact temperatures can be expected. Certain solid lubricants on a fluoride base are also able to ensure the lubrication reliably under these critical conditions. Calcium fluorides, CaF₂, and barium fluorides, Ba₂, can thus e.g. reliably ensure the lubrication even at locally occurring temperatures of up to more than 1200° C. In this respect, the eutectic form 62% by weight BaF₂ and 38% by weight CaF₂ has proved particularly effective which already ensures a considerably improved lubrication from 500° C.

It has been shown in this respect that, depending on the specific engine type, different compositions of iron titanate layers FeTiO₃ (ilmenite) and solid lubricant can advantageously be used. Some typical examples are shown by way of example in the following Table 1. The data in this respect above all apply to the internal coating of the cylinder running surface of these engines.

TABLE 1 Typical applications examples; combinations of solid lubricant additives in iron titanate layers FeTiO₃ Sulfide Nitride Fluoride Type of [Vol. [Vol. [Vol. Typical engine Type of load %] %] %] application Gasoline Higher speeds 6 3 1 Sports car engines Regular with 4-stroke performance automatic Water cooling Gasoline Higher speeds 5 2 3 Racing engines Highly changing engines 4-stroke performance Water cooling Gasoline Higher speeds 3 4 3 Karting engines Highly changing engine 2 and 4 performance Motorcycles stroke Air cooling Gasoline Medium speeds 4 5 1 Current engines Regular generator 4-stroke performance Air cooling Diesel Regular 5 4 1 Ship diesel engines speeds Current 2-4 stroke Regular generator performance Diesel Highly changing 4 4 2 Truck and engines performance and automobile 4-stroke speeds Diesel Adiabatic engine 1 3 6 Military engines Higher operating vehicles temperature Modern generation

On the coating of cylinder running surfaces e.g. with the aid of an F-210 plasma torch, a powder yield of 60 to 70% can be expected. The specific weight of the corresponding layers should be around 4 g/cm³.

Conveying rates up to 80 g/min can be achieved provided that the powder conveying system is optimally designed. A distribution of 5 to 30 micrometers is advantageous as a powder particle size. The maximum layer thickness is influenced by a plurality of factors (material substrates, coating parameters, E-modulus of the layers, etc.). The use of an intermediate layer is often not necessary on cast iron or steel substrates, apart from cases where a strong corrosion is to be feared. With aluminum base alloys, an intermediate layer of NiCr alloys and/or NiAl alloys has proved to be advantageous.

The thermally sprayed layers are advantageously reworked in a known manner by diamond honing.

In a particularly preferred embodiment of a spray material in accordance with the invention, the volume portion of sulfide amounts to 0.1% to 15% volume percent, preferably 1% to 6% volume percent, with the sulfide in a specific embodiment only being, except for contaminants, MoS₂ and/or WS₂.

The volume portion of fluoride can advantageously amount to from 0.05% to 20% volume percent, preferably from 1% to 10% volume percent, with the fluoride only being, except for contaminants, CaF₂ and/or BaF₂ in a specific embodiment.

As already mentioned, CaF₂ and BaF₂ are preferably, but not necessarily, present as a eutectic.

In a particularly preferred embodiment, a spray material in accordance with the invention is only composed of, except for contaminants, a sulfide, a fluoride and the remainder FeTiO₃ as a base material.

In this respect, the spray material can additionally also include a nitride as a solid lubricant for covering specific temperature loads, with the volume portion of nitride advantageously being from 0.1% to 8% volume percent, preferably from 1% to 5% volume percent. In this respect, only hexagonal BN and/or CN is particularly preferably used in a spray material in accordance with the invention.

In this respect, in another variant, the spray material of the present invention can also only be composed of, except for contaminants, a nitride, a sulfide, a fluoride and the remainder FeTiO₃ as a base material.

If the spray material in accordance with the invention is present as a powder material for use in a thermal spraying process, a grain size distribution of the powder material is preferably between 2 μm and 60 μm, in particular between 5 μm and 40 μm.

To manufacture a spray material in accordance with the present invention, the base material FeTiO₃ is in this respect manufactured by grinding and/or screening in a manner known per se from ilmenite, with the base material FeTiO₃ also first being able to be remelted before the grinding and/or screening.

In a preferred embodiment variant of a manufacturing process in accordance with the invention, at least one of the solid lubricants is formed in the form of solid lubricant particles and is agglomerated by spray drying and/or cladding with particles of the base material FeTiO₃.

The invention in this respect also relates to a spray wire, in particular a spray filler wire, for use in a thermal wire spraying process including a spray material of the invention.

The invention further relates to a thermal spray layer on an iron base for a substrate, in particular for a running surface of a cylinder of a reciprocating combustion engine, with the thermal spray layer including FeTiO₃ as a base material. In accordance with the invention, the thermal spray layer includes at least one first solid lubricant composed of a sulfide and one second solid lubricant composed of a fluoride.

In a thermal spray layer of the present invention, the volume portion of sulfide preferably amount to 0.1% to 15% volume percent, preferably 1% to 6% volume percent, with the sulfide specifically being able only to be, except for contaminants, MoS₂ and/or WS₂

In a further embodiment, the volume portion of fluoride in the thermal spray layer preferably amounts to 0.05% to 20% volume percent, preferably 1% to 10% volume percent, with preferably, but not necessarily, the fluoride only being, except for contaminants, CaF₂ and/or BaF₂ and/or CaF₂ and BaF₂ being able to be present as a eutectic.

In a specific embodiment, the thermal spray layer can be composed only of, except for contaminants, a sulfide, a fluoride and the remainder of FeTiO₃ as a base material.

In a further embodiment, the thermal spray layer in accordance with the invention can additionally include a nitride, with the volume portion of nitride being able to amount, for example, to 0.1% to 8% volume percent, preferably 1% to 5% volume percent, and/or with the nitride specifically being only hexagonal BN and/or CrN.

In a particularly preferred embodiment, the thermal spray layer of the present invention is composed only of, except for contaminants, a nitride, a sulfide, a fluoride and the remainder of FeTiO₃.

The invention further relates to a spraying method for manufacturing a thermal spray layer in accordance with the present invention, with the spraying method being a thermal spraying method, in particular a plasma spraying method.

In another embodiment, the thermal spraying method can also be a flame spraying method, an HVOF spraying method, specifically a powder spraying method or a wire spraying method, or another thermal spraying method known per se.

The invention furthermore also relates to the use of a spray powder or of a spray wire from a spray material of the invention for manufacturing a thermal spray layer in accordance with the invention.

It can be stated in summary that iron titanate FeTiO₃ which is composed of approximately 53% by weight TiO₂ and 47% FeO and crystallizes in a hexagonal crystal system was also known per se in the prior art for the use on cylinder running surfaces of internal combustion engines due to its tribological properties.

Today, approximately 5000 metric tonnes of ilmenite are processed worldwide every year, above all for the manufacture of pigments from titanium oxides and for the manufacture of metallic titanium. The most important deposits are in Australia, Canada, South Africa, China, Norway; larger deposits in Madagascar and Mozambique are hardly used.

At the end of 2008, the price of ilmenite minerals was at US C120 per metric tonne. In the further processing into sprayable powder (washing, grinding and screening), only relatively low further costs are to be expected so that currently manufacturing costs of approximately US $5 per kg can be expected, plus the costs for the solid lubricants.

However, it was able to be shown for the first time by the present invention that an exceptionally suitable raw material is available with the raw material ilmenite for the simple and economic manufacture of an iron titanate spray powder. The addition of solid lubricants such as nitrides (hexagonal BN, CrN), sulfides (MoS₂, WS₂), fluorides (CaF₂, BaF₂) or suitable combinations thereof allow elevated wall temperatures of the cylinders of internal combustion engines. The requirements for the construction and secure operation of adiabatic engines are thus also realized under extreme temperature conditions for the first time. 

1. A spray material based on iron for the thermal coating of a substrate, in particular for the thermal coating of a running surface of a cylinder of a reciprocating combustion engine, wherein the spray material includes FeTiO₃ as a base material, characterized in that the spray material includes at least one first solid lubricant composed of a sulfide and one second solid lubricant composed of a fluoride.
 2. A spray material in accordance with claim 1, wherein the proportion by volume of sulfide amounts to 0.1% to 15% by volume, preferably 1% to 6% by volume.
 3. A spray material in accordance with claim 1, wherein the sulfide is only MoS₂ and/or WS₂, except for contaminants.
 4. A spray material in accordance with claim 1, wherein the proportion by volume of fluoride mounts to 0.05% to 20% by volume, preferably 1% to 10% by volume.
 5. A spray material in accordance with claim 1, wherein the fluoride is only CaF₂ and/or BaF₂, except for contaminants.
 6. A spray material in accordance with claim 5, wherein CaF₂ and BaF₂ are present as a eutectic.
 7. A spray material in accordance with any one of the preceding claims claim 1, wherein the spray material is composed only of, except for contaminants, a sulfide, a fluoride and the remainder FeTiO₃ as a base material.
 8. A spray material in accordance with claim 1, wherein the spray material additionally includes a nitride.
 9. A spray material in accordance with claim 8, wherein the proportion by volume of nitride amounts to 0.1% to 8% by volume, preferably 1% to 5% by volume.
 10. A spray material in accordance with claim 8, wherein the nitride is only hexagonal BN and/or CrN.
 11. A spray material in accordance with claim 8, wherein the spray material is composed only of, except for contaminants, a nitride, a sulfide, a fluoride and the remainder FeTiO₃ as a base material.
 12. A spray material in accordance with claim 1, wherein the spray material is a powder material having a grain size distribution between 2 μm and 60 μm, preferably between 5 μm and 40 μm
 13. A spray material in accordance with claim 1, wherein the spray material is a spray powder for thermal spraying.
 14. A method of manufacturing a spray material in accordance with claim 1, wherein the base materials FeTiO₃ is manufactured by grinding and/or screening from ilmenite.
 15. A method in accordance with claim 14, wherein the base material FeTiO₃ is first remelted before the grinding and/or screening.
 16. A method in accordance with claim 14, wherein at least one of the solid lubricants is formed in the form of solid lubricant particles and is agglomerated by spray drying and/or cladding with particles of the base material FeTiO₃.
 17. A spray wire for use in a thermal wire spraying method including a spray material in accordance with claim
 1. 18. A thermal spray layer based on iron for a substrate, in particular for a running surface of a cylinder of a reciprocating combustion engine, wherein the thermal spray layer includes FeTiO₃ as a base material, characterized in that the thermal spray layer includes at least one first solid lubricant composed of a sulfide and one second solid lubricant composed of a fluoride.
 19. A thermal spray layer in accordance with claim 18, wherein the proportion by volume of sulfide amounts to 0.1% to 15% by volume, preferably 1% to 6% by volume.
 20. A thermal spray layer in accordance with claim 18, wherein the sulfide is only MoS₂ and/or WS₂, except for contaminants.
 21. A thermal spray layer in accordance with claim 18, wherein the proportion by volume of fluoride amounts to 0.05% to 20% by volume, preferably 1% to 10% by volume.
 22. A thermal spray layer in accordance with claim 18, wherein the fluoride is only CaF₂ and/or BaF₂, except for contaminants.
 23. A thermal spray layer in accordance with claim 22, wherein CaF₂ and BaF₂ are present as a eutectic.
 24. A thermal spray layer in accordance with claim 18, wherein the thermal spray layer is composed only of, except for contaminants, a sulfide, a fluoride and the remainder of FeTiO₃ as a base material.
 25. A thermal spray layer in accordance with claim 18, wherein the thermal spray layer additionally includes a nitride.
 26. A thermal spray layer in accordance with claim 25, wherein the proportion by volume of nitride amounts to 0.1% to 8% by volume, preferably 1% to 5% by volume.
 27. A thermal spray layer in accordance with claim 25, wherein the nitride is only hexagonal BN and/or CrN.
 28. A thermal spray layer in accordance with claim 25, wherein the thermal spray layer is composed only of, except for contaminants, a nitride, a sulfide, a fluoride and the remainder of FeTiO₃ as a base material.
 29. A spraying method of manufacturing a thermal spray layer in accordance with claim 18, wherein the spraying method is a thermal spraying method.
 30. A spraying method in accordance with claim 29, wherein the thermal spraying method is a plasma spraying method.
 31. A spraying method in accordance with claim 29, wherein the thermal spraying method is a flame spraying method.
 32. A spraying method in accordance with claim 29, wherein the spraying method is a powder spraying method or a wire spraying method.
 33. Use of a spray powder composed of a spray material in accordance with claim 1 for manufacturing a thermal spray layer.
 34. Use of a spray wire in accordance with claim 17 for manufacturing a thermal spray layer. 